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Nicely balooned screen
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    Everybody knows that hydraulic pumps are expensive, especially closed loop pumps. And everybody is aware that hydraulic circuits are dirt-sensitive, especially closed loops. The ones who had already performed the thrilling task of mounting a closed loop transmission (in this case on board a BIG ship) which includes 180cc 200kg pumps, know that it is time and effort consuming process. In fact, you should think twice before you utter anything even remotely suggesting a slightest possibility of having to remove the recently mounted "pumping unit", to the team who had taken two full days just to fit it in place, with the help of torch, hammer, the God and God knows what, if you want to keep your health and looks intact. (yeah, I AM participating in "the longest sentence contest", if you must know). Apart from time and effort, a closed loop set-up consumes tons of money. That is why it is so important to make sure that everything works OK first-time.

     THE most important part of a closed circuit start-up preparation is the THOROUGH cleaning and flushing of the entire circuit. Most of the times a simple flushing procedure with pressure filters and sensitive components by-passing is enough. I am smiling now, I just said  "simple flushing", it is never simple. But sometimes, when the piping is extensive, welded or exposed to the elements during several months construction process, used as ash-tray/toilet during construction, you name it, a cleaning should be yet thorough-er.

    I, myself, have already performed such an exciting super-flushing operation (on a fishing boat, by the way, it was a winch driving circuit). We first used special acid solution pumped by an external centrifugal pump, then an alkaline acid removing solution, then water, then oil, then oil again, and lots and lots of F words during the process... Believe me, the cost of those pumps (both on main and auxiliary engines) and motors left no margin for error. The start up went smoothly in a "by the book" fashion.

    Nevertheless, sometimes the cleaning is overlooked. Which is a feast for us, pump/motor guys, as in this case an expensive overhaul is guaranteed! Check out the pics. This pump has around half an our work time. In the end it stopped responding to the control signal because the Pressure Control Pilot valve screen got completely clogged (pic1), creating the beautiful ballooned shape. Some measurements were made, the PCP was dismounted from the control valve and the filter exposed. At this time I suggested that further pump testing was senseless, and still the client insisted on a bench test. O.K says I! PCP gets a new filter, four hours later the pump responds to the external signal on the test bench but looses charge pressure at 100 bar high. Well, told you...

    Exposing the  insides revealed severe contamination damage and many small metal balls, originated from welding sparks. Want to take a wild guess on how the piping had been made? (It was welded, dah!)

    The pump, parts of which you see on the pics was the first of a set of four.... all four went the same way...  Quite a kick in the nuts, don't you agree?